Green’s Dictionary of Slang

to defecate.

1593		Passionate Morrice (1876) 75: Shee would hang about his neck before all that company, as a iacke of Napes doth sitting on the bear-heards shoulder, and kisse as openly, as a dog scombers carelessly.
1629		Massinger Picture V i: Just such a one as you use to a brace of gray-houndes, When they are ledd out of their kennels to scumber.
1656		Mennis & Smith ‘To a friend upon a jouney to Epsam Well’ Musarum Deliciae (1817) 10: But he that gains the glory here / Must scumber furthest, shite most clear.
1696		Motteux (trans.) Gargantua and Pantagruel (1927) II Bk IV 422: I happened to read a chapter [...] and old Nick turn me into bumfodder, if this did not make me so hide-bound and costive, that for four or five days I hardly scumbered one poor butt of sir-reverance.